Background Information

Many materials are hydrophobic (water-fearing) in nature. Due to their non-polar chemical structure, hydrophobic particles want to minimize contact with polar (water) molecules and, as a result, tend to aggregate on the surface of the water and resist going into suspension. This presents a challenge to scientists and engineers who would like to be able to work with hydrophobic particles suspended in aqueous solution.

Fortunately, there is a simple way to overcome the hydrophobic effect. It is called a surfactant, a detergent, or simply “soap.” Surfactant is a magical molecule that has both hydrophobic and hydrophilic properties, which coats the particles and helps them mix into water. The same mechanism applies when we use soap to wash greasy dishes or stained clothes.

Selection of the surfactant depends purely on your process and product requirements. Dishwashing liquid works great, so does Simple Green. For scientists working on biological applications we recommend the use of Tween surfactants. Tween is the commercial name for Polysorbate non-ionic surfactants, which are stable, nontoxic, and often used in pharmacological, cosmetic, and food applications. Non-ionic detergents are considered to be “mild” detergents because they are less likely than ionic detergents to denature proteins. By not separating protein-protein bonds, non-ionic detergents allow the protein to retain its native structure and functionality.

Tween 20 and Tween 80 are frequently used. Both surfactants are yellowish, water-soluble viscous liquids. Primary difference between the two is viscosity. Tween 20 has lower viscosity and is easier to work with.

Suspension Process

There are many ways to suspend the particles (e.g. put a few drops of dish detergent into water and shake with the particles).

The process below is specific for using the minimum amount of Tween for biologically sensitive applications.

Safety:

Gloves and eye protection are to be worn at all times during solution preparation and use.

Care should be taken when handling hot objects/liquids and immersion blender.

Centrifuge should be properly balanced and allowed to come to a full stop before opening.

Recommendations:

We recommend using distilled water to minimize impurities.

We recommend boiling the water to sterilize and to make it easier to disperse a small amount of surfactant uniformly. This also increases shelf-life of prepared solutions and suspensions.

We use an immersion blender to disperse the surfactant in water quickly and effectively.

Process:

Preparing Tween Solution:

Fill a heatproof container with distilled water.

Ensure the water level is high enough to cover the immersion blender.

Heat water to boiling and leave boiling for 5 minutes.

Weigh out 0.1g of Tween per 100ml of water used (creating 0.1% solution).

Slowly add Tween to boiled water while mixing with immersion mixer (~30 seconds).

Some bubbles will form during mixing.

Bubbles will dissipate on cooling and solution will appear clear.

Suspending particles in Tween solution.

Place the desired amount of particles into a container.

Dispense prepared Tween solution on top of particles.

We recommend at least five times greater volume of solution to the volume of particles.

Cover tightly and place containers into a centrifuge.

Centrifuge on highest setting for at least 5 minutes.

If some particles are still floating on the surface of water, more centrifuging may be necessary.

A small quantity of particles may accumulate on the top surface and not enter solution despite additional centrifugation. Typically, these particles will go into suspension over time (hours).

Other Considerations

A greater length of centrifuging or larger volume of Tween solution may be necessary to suspend certain materials and particle sizes.

As a 0.1% Tween solution is sufficient for most applications, concentration levels could be raised to support particles that are more resistant to entering solution.

Once the particles are suspended, solution can may be diluted further to increase the volume.

Particles can be recycled and reused as necessary. The suspension might need to be repeated.

If no centrifuge is available, it is possible to shake the container by hand (up and down, upside down) to achieve the same result.

Here is an example of Cospheric fluorescent beads 150 to 180micron in diameter being dispersed in a pilot bioreactor.

About Cospheric

Our extensive product line consists of more than two thousand unique spherical microparticle and nanoparticle products, all developed based on customer demand. We work with each individual customer to find a creative solution for their unique needs ­– tight particle size ranges, wide selection of colors, densities, properties and formulations. We are the sole global supplier for the majority of our products. We developed a disruptive technology which is redefining the microsphere market and creating a new category of precision spherical particles. Our research department is always excited to tackle new challenging projects. Explore at www.Cospheric.com.

Other Information

The information contained in this document is correct to the best of our knowledge at the date of publication. It should not be viewed as all inclusive, but as a guide only. It does not represent any guarantee of the properties of the product. Cospheric LLC shall not be held liable for any damage resulting from handling of or from contact with the above product. For these reasons, it is important that product users carry out their own tests to satisfy themselves as to the suitability of the safety precautions for their own intended applications.

Density Marker Beads Kit Now Available from Cospheric LLC

Santa Barbara, CA, December 6, 2013 – Cospheric LLC, a microsphere manufacturing and distributing company, expanded their line of density marker beads which now offers six different densities including 1.02 g/cc (fluorescent green), 1.04g/cc (fluorescent orange), 1.06g/cc (fluorescent violet), 1.08 g/cc (dark blue), 1.09 g/cc (fluorescent red), and 1.13g/cc (fluorescent blue). Cospheric Density Marker Beads are now provided at a 20% concentration in an aqueous solution in 2.5ml vials, which makes the spheres easier to work with for the customers. Microspheres of different densities can be purchased individually or as a density marker beads kit.

Microspheres of accurately known mass density are generally used as an external marker to facilitate the monitoring of the density gradient shape and range. Density marker beads enable excellent stratification and bright coloration for high visibility with the unaided eye. Historically density calibration beads in the size ranges of 212-250um or 250-300um are used. Unlike the discontinued density marker kits which used to be manufactured by GE Healthcare and sold by Sigma-Aldrich, Cospheric’s DMB density marker beads are ready for use right out of the vial, don’t need to be swollen, do not expire, and do not change density over time. Cospheric’s DMB microspheres will create Percoll gradients but will also work with any other centrifugation media. The colored microbeads may be recovered and stored for future use.

The density marker beads provide a rapid, simple, and accurate method for measuring the density. Generally a set of several such beads, covering a range of densities, is used. In the biomedical industry researchers are sometimes looking for cells having targeted specific gravities. In order to locate these cells in test tubes it is useful to have colored marker beads which will show where the delineation between specific densities occurs. Density marker beads are also used for calibrating particles in other industries, such as agriculture, microbiology and others.

About Cospheric LLC:
Cospheric LLC develops, manufactures, and distributes high-quality microspheres in sizes from 10 micron to 1000 micron (1mm). Cospheric specializes in polyethylene microspheres and carries a large stock of polyethylene microspheres in many colors, fluorescent, phosphorescent, neutrally-buoyant, and paramagnetic properties. Cospheric also offers a selection of soda-lime and borosilicate glass, silica, metal-coated, and titanium dioxide-coated spheres, some available in spacer grades with very tight particle size distributions. Cospheric LLC welcomes inquiries for custom manufacturing of microspheres tuned to each customer’s unique specifications. Cospheric is an eco-friendly company that uses only recyclable materials and no solvents in the manufacturing process. For more information, pricing and sample requests visit www.cospheric.com.

About Microspheres:
Microspheres or beads are spherical particles usually between 1 to 1000 microns in diameter and are manufactured for wide variety of uses in research, medicine, consumer goods, paints and coatings, adhesives, personal care, household products, cosmetics, skin care, and other industries.

Density Marker Beads

Cospheric recently added density marker beads in aqueous solution to their range of products. Available in densities from 1.02 g/ml to 1.13 g/ml.

The beads come in a variety of colors and densities and ship within one business day. These beads are small microspheres of very specific particle density that are used to visualize density gradients. Commonly used in Percoll gradients these beads offer a fast visual indicator for scientists.

Cospheric Density Marker Beads are provided at a 20% concentration in an aqueous solution in 2.5ml vials. Unlike density marker kits which used to be manufactured by GE Healthcare and have been discontinued, the Cospheric’s colored microspheres are ready for use right out of the vial, don’t need to be swollen, will work with any media, do not expire, and do not change density over time.

Resources on Creating Density Gradients:

Biotechnology: Theory and Techniques, Volume I (Jones and Bartlett Series in Biology) by Jack Chirikjian and Chirikjian (Jan 1, 1995)
Pages 45-50 on Density Gradient Centrifugation.